This invention relates generally to the development of electrostatic images, and more particularly concerns a scavengeless development system in which an asymmetrical electrical bias is applied on the electrode wires.
The invention can be used in the art of electrophotographic printing. Generally, the process of electrophotographic printing includes sensitizing a photoconductive surface by charging it to a substantially uniform potential. The charge is selectively dissipated in accordance with a pattern of activating radiation corresponding to a desired image. The selective dissipation of the charge leaves a latent charge pattern that is developed by bringing a developer material into contact therewith. This process forms a toner powder image on the photoconductive surface which is subsequently transferred to a copy sheet. Finally, the powder image is heated to permanently affix it to the copy sheet in image configuration.
Two component and single component developer materials are commonly used. A typical two component developer material comprises magnetic carrier granules having toner particles adhering triboelectrically thereto. A single component developer material typically comprises toner particles having an electrostatic charge so that they will be attracted to, and adhere to, the latent image on the photoconductive surface.
There are various known development systems for bringing toner particles to a latent image on a photoconductive surface. Single component development systems use a donor roll for transporting charged toner to the development nip defined by the donor roll and the photoconductive surface. The toner is developed on the latent image recorded on the photoconductive surface by a combination of mechanical scavengeless development. A scavengeless development system uses a donor roll with a plurality of electrode wires closely spaced therefrom in the development zone. An AC voltage is applied to the wires detaching the toner from the donor roll and forming a toner powder cloud in the development zone. The electrostatic fields generated by the latent image attract toner from the toner cloud to develop the latent image. In another type of scavengeless system, a magnetic developer roll attracts developer from a reservoir. The developer includes carrier and toner. The toner is attracted from the carrier to a donor roll. The donor roll then carries the toner into proximity with the latent image.
A problem with the scavengeless development system is that of wire movement, referred to as strobing. Wire strobing occurs when the interaction between the scavengeless wires, wire AC voltage, donor roll and toner materials creates a condition wherein the wires physically oscillate causing a quality defect in the developed image.
The following disclosures may be relevant to various aspects of the present invention:
U.S. Pat. No. 4,102,305. Patentee: Schwarz. Issued: Jul. 25, 1978. PA0 U.S. Pat. No. 4,565,438. Patentee: Folkins. Issued: Jan. 21, 1986. PA0 U.S. Pat. No. 4,868,600. Patentee: Hays et al. Issued: Sep. 19,1989. PA0 Co-pending U.S. patent application Ser. No. 07/563,026. Applicant: Floyd Jr. et al. Filed: Aug. 3, 1990.
The relevant portions of the foregoing disclosures may be briefly summarized as follows:
U.S. Pat. No. 4,102,305 describes a developer roll that is electrically biased with an AC voltage superimposed over a DC voltage.
U.S. Pat. No. 4,565,438 discloses an asymmetrical alternating electrical bias applied on a developer roller.
U.S. Pat. No. 4,868,600 describes a scavengeless development system in which toner is detached from a donor roll and a powder cloud obtained by AC electrically biased electrode wires. The donor roll is electrically biased by a DC voltage.
Co-pending U.S. patent application Ser. No. 07/563,026 describes a magnetic roll for transporting developer material from a reservoir to a donor roll and electrode wires that are electrically biased to detach toner from the donor roll so as to form a toner cloud in the development zone.